There is nothing in that circuit to change the frequency. The sole purpose is to adjust the gin versus frequency relationship. THAT is why the controls are tagged "Bass boost" and "Bass cut," "Trebles Boost" and "Treble cut."

Do you really think I don't know that?

 

OK,f I misread the post, my error and my apology. Certainly now I see that it does say response. How could I have missed that ???
I removed the post. It was totally wrong. I blame my fatigue at the time.

 

Does the output frequency response change with movement of either pot?

Very little. Only at 90% rotation and above.

 

Very little. Only at 90% rotation and above.

This is useful information! It implies that the effect of the frequency sensitive elements is present but inadequate. In this case that would be that either the capacitance values do not match those that work in the simulation, or that the resistances in series with them are incorrect, probably excessive. Checking resistor values with a DMM is a simple first step.

 

This is useful information! It implies that the effect of the frequency sensitive elements is present but inadequate. In this case that would be that either the capacitance values do not match those that work in the simulation, or that the resistances in series with them are incorrect, probably excessive. Checking resistor values with a DMM is a simple first step.

I have done that. The 560pf cap is off by 10pf. Hence, it’s 550pf which I think shouldn’t be an issue.

 

Hi aneves.
Are you using linear or logarithmic range potentiometers, for the Bass and Treble?

E

 

Hi aneves.
Are you using linear or logarithmic range potentiometers, for the Bass and Treble?

E

I thought of that. The pots are marked B100K which indicates that they are linear.

TS can confirm linear or log by testing.
Remove the pot from the circuit and set it to middle rotation. Measure the resistance from centre pin to left pin, again from centre pin to right pin.

 

ANY of the fixed resistors could also be an issue.

 

I've made some progress. The treble control seems to be working well for frequency > 1.5khz. The base control does not work at all for frequencies below < 500hz; I am getting a signal though but no response when dialing the bass potentiometer. Again have checked an rechecked my component values and they are right on.

I'm measuring the output of the network at the inverting input of the op-amp not the output. The reason is the output of the op-amp is not acting like a buffer as it should. When vary both controls there is no change at the op-amp output. But I can see the change of the treble control at the inverting input of the op-amp. I have swapped out op-amps and I'm getting the same result. Which leads me to believe that there maybe a breadboard fault in that location that I have the op-amp inserted into. I will try moving it to a different location. I guess patience and determination is the key.

I will keep everyone posted.

 

You cannot measure the signal at the input of the op amp.

The non-inverting input is set to a reference voltage.
The voltage at the inverting input must be equal to the voltage at the non-inverting input. That is how op amps work since the op amp open loop voltage gain is very high, greater than 100,000.

 

Hi aneves.
Are you using linear or logarithmic range potentiometers, for the Bass and Treble?

E

Linear.

 

Im starting to believe that a good percentage of the problem is that crappy breadboard that I’m using. I guess I’m going to have to start perf boarding and soldering to do proof of concept.

 

Im starting to believe that a good percentage of the problem is that crappy breadboard that I’m using. I guess I’m going to have to start perf boarding and soldering to do proof of concept.

If you've double-checked all the wiring on your breadboard both visually and using an ohmmeter, then that likely is your best next step.

One problem could be the small wires on your resistors, which may not be making good connection with the breadboard contacts.

 

If you've double-checked all the wiring on your breadboard both visually and using an ohmmeter, then that likely is your best next step.

One problem could be the small wires on your resistors, which may not be making good connection with the breadboard contacts.

Yeah, I know those cheap Chinese resistors. I’ve looked for a good source of made in the USA assorted multipacks. Some what hard to find limited supply and or expensive.

 

I think that you have verified that all of the resistor values are as marked. Wrong values can seriously affect circuit operation.

 

I think that you have verified that all of the resistor values are as marked. Wrong values can seriously affect circuit operation.

Did that and checked all values with DMM.

 

Did that and checked all values with DMM.

Thank you everyone for your help.

 

Hopefully, this thread is still open. The resistor and cap network behaves like a bass/treble cut/boost at the C1 capacitor that feeds into the inverting input of the op-amp. But the the output from the op-amp is not responding as a buffer. I swapped out op-amps that didn't solve the problem.

 

What values have been assigned to R2,3,6,7?
What are the voltages of Vin, Vbias, Vcc, Vout?

 

the output from the op-amp is not responding as a buffer.

Then the circuit won't work properly, since it depends upon negative feedback from the op amp output to the filter components to generate the filter functions.
The op amp is not a buffer, it acts as an inverting amp.
Why would you think the tone control would work if the op amp wasn't?